When drilling or completing wells in earth formations, various fluids typically are used in the well for a variety of reasons. For purposes of description of the background of the invention and of the invention itself, such fluids will be referred to as “well fluids.” Common uses for well fluids include: lubrication and cooling of drill bit cutting surfaces while drilling generally or drilling-in (i.e., drilling in a targeted petroleum bearing formation), transportation of “cuttings” (pieces of formation dislodged by the cutting action of the teeth on a drill bit) to the surface, controlling formation fluid pressure to prevent blowouts, maintaining well stability, suspending solids in the well, minimizing fluid loss into and stabilizing the formation through which the well is being drilled, fracturing the formation in the vicinity of the well, displacing the fluid within the well with another fluid, cleaning the well, testing the well, implacing a packer fluid, abandoning the well or preparing the well for abandonment, and otherwise treating the well or the formation.
As stated above, one use of well fluids is the removal of rock particles (“cuttings”) from the formation being drilled. A problem arises in disposing these cuttings, particularly when the drilling fluid is oil-based or hydrocarbon-based. That is, the oil from the drilling fluid (as well as any oil from the formation) becomes associated with or adsorbed to the surfaces of the cuttings. The cuttings are then an environmentally hazardous material, making disposal a problem.
A variety of methods have been proposed to remove adsorbed hydrocarbons from the cuttings. U.S. Pat. No. 5,968,370 discloses one such method which includes applying a treatment fluid to the contaminated cuttings. The treatment fluid includes water, a silicate, a nonionic surfactant, an anionic surfactant, a phosphate builder and a caustic compound. The treatment fluid is then contacted with, and preferably mixed thoroughly with, the contaminated cuttings for a time sufficient to remove the hydrocarbons from at least some of the solid particles. The treatment fluid causes the hydrocarbons to be desorbed and otherwise disassociated from the solid particles.
Furthermore, the hydrocarbons then form a separate homogenous layer from the treatment fluid and any aqueous component. The hydrocarbons are then separated from the treatment fluid and from the solid particles in a separation step, e.g., by skimming. The hydrocarbons are then recovered, and the treatment fluid is recycled by applying the treatment fluid to additional contaminated sludge. The solvent must be processed separately.
Some prior art systems use low-temperature thermal desorption as a means for removing hydrocarbons from extracted soils. Generally speaking, low-temperature thermal desorption (LTTD) is an ex-situ remedial technology that uses heat to physically separate hydrocarbons from excavated soils. Thermal desorbers are designed to heat soils to temperatures sufficient to cause hydrocarbons to volatilize and desorb (physically separate) from the soil. Typically, in prior art systems, some pre- and post-processing of the excavated soil is required when using LTTD. In particular, excavated soils are first screened to remove large cuttings (e.g., cuttings that are greater than 2 inches in diameter). These cuttings may be sized (i.e., crushed or shredded) and then introduced back into a feed material. After leaving the desorber, soils are cooled, re-moistened, and stabilized (as necessary) to prepare them for disposal/reuse.
U.S. Pat. No. 5,127,343 (the '343 patent) discloses one prior art apparatus for the low-temperature thermal desorption of hydrocarbons. FIG. 1 from the '343 patent reveals that the apparatus consists of three main parts: a soil treating vessel, a bank of heaters, and a vacuum and gas discharge system. The soil treating vessel is a rectangularly shaped receptacle. The bottom wall of the soil treating vessel has a plurality of vacuum chambers, and each vacuum chamber has an elongated vacuum tube positioned inside. The vacuum tube is surrounded by pea gravel, which traps dirt particles and prevents them from entering a vacuum pump attached to the vacuum tube.
The bank of heaters has a plurality of downwardly directed infrared heaters, which are closely spaced to thoroughly heat the entire surface of soil when the heaters are on. The apparatus functions by heating the soil both radiantly and convectionly, and a vacuum is then pulled through tubes at a point furthest away from the heaters. This vacuum both draws the convection heat (formed by the excitation of the molecules from the infrared radiation) throughout the soil and reduces the vapor pressure within the treatment chamber. Lowering the vapor pressure decreases the boiling point of the hydrocarbons, causing the hydrocarbons to volatize at much lower temperatures than normal. The vacuum then removes the vapors and exhausts them through an exhaust stack, which may include a condenser or a catalytic converter.
In light of the needs to maximize heat transfer to a contaminated substrate using temperatures below combustion temperatures, U.S. Pat. No. 6,399,851 discloses a thermal phase separation unit that heats a contaminated substrate to a temperature effective to volatize contaminants in the contaminated substrate but below combustion temperatures. As shown in FIGS. 3 and 5 of U.S. Pat. No. 6,399,851, the thermal phase separation unit includes a suspended air-tight extraction, or processing, chamber having two troughs arranged in a “kidney-shaped” configuration and equipped with rotating augers that move the substrate through the extraction chamber as the substrate is indirectly heated by a means for heating the extraction chamber.
In addition to the applications described above, those of ordinary skill in the art will appreciate that recovery of adsorbed hydrocarbons is an important application for a number of industries. For example, a hammermill process is often used to recover hydrocarbons from a solid. One recurring problem, however, is that the recovered hydrocarbons, whether they are received by either of the methods described above or whether by another method, can become degraded, either through the recovery process itself, or by the further use of the recovered hydrocarbons.
This degradation may result in pungent odors, decreased performance, discoloration, and/or other factors which will be appreciated by those having ordinary skill in the art. What is needed, therefore, are methods and apparatuses for improving the properties of recovered hydrocarbons.